Copolymers comprising polysiloxane moieties are known to possess desirable properties. Coatings of such copolymers are very adhesive and water repellent, while remaining fairly scratch resistant. The copolymers do also possess desirable slip and anti-sticking properties.
In, e.g., EP-A 118 387 and EP-A 188 388 polyesters, modified with polysiloxane moieties and having good slip properties, are disclosed. The polysiloxane moieties are polysiloxane-polyethers and are di-hydroxy-terminated. The incorporation of the polysiloxane moieties in the polyester proceeds by polycondensation of the polysiloxane diol together with di-carboxylic acids and other diols.
In, e.g., EP-A 380 224, a thermal transfer donor element is disclosed, comprising an anti-sticking backing layer, wherein an organopolysiloxane-polyurea is incorporated. These copolymers are prepared by the reaction of a silicone diamine, a di-isocyanate and a diamine or dihydroxy chain extender.
The use of copolymers comprising polysiloxane moieties in toner particles used as image forming species in electrically or magnetically based imaging methods is also known. Said copolymers are mainly used to overcome adhesion problems typical for toner particles. The adhesion of toner particles to each other, diminishing fluidity of the toner and diminishing resolution in the final image is one of the problems addressed by using copolymers comprising polysiloxane moieties. An other problem addressed by the use of said copolymers, is, in a multi-component developer, the adhesion of toner particles to carrier particles. Also the problem of "hot-offset" in imaging methods using a heated fixing roller can be overcome by using the copolymers described above.
In DE-OS 22 53 402 it is disclosed to use a block copolymer comprising a hard block and a weak block to overcome problems with hot-offset. The choice of the preferred hard and weak blocks depends more on the elasticity modulus and/or tensile strength than by the chemical nature of the hard and weak blocks. A copolymer comprising poly(bisphenol A-carbonate) as hard block and polydimethylsiloxane as weak block is disclosed.
In U.S. Pat. No. 5,089,547 the use of low surface adhesion (LSA) additives in toner composition is disclosed. The LSA are cross-linked and formed by the reaction of an aminoterminated polysiloxane, a polyester and a novolac resin carrying epoxy groups. Di-functional secondary amine terminated polysiloxanes are preferred.
In EP-A 298 279 it is disclosed that toner particles, comprising a mixture of polyester resin and a polyester resin comprising polysiloxane chains (cross-linked or not) as toner resin, are very well suited for use in imaging systems using a hot roller fusing step. It is also stated, in e.g. EP-A 298 279, that the quality of the blending of both resins, during the toner preparation, influences the quality of the toner particles and the amount of polysiloxane modified polyester needed in the toner particles. In EP-A 298 279 the preparation of a random graft polymer of a multifunctional organosiloxane polymer, namely .alpha., .omega., .delta.-aminopropyl poly(dimethyl-co-methoxy-.delta.-aminopropyl siloxane) and a polyester is described. The reaction proceeds at 220.degree. C. for 2 hours followed by another hour reaction at 240.degree. C. and under reduced pressure. The incorporation of polysiloxane moieties in polyesters over an amino group, is not so desirable for polysiloxane modified resins used as toner resin, since polyester tend to be negatively charged by tribo-electric contact and the aminogroups diminish the negative chargeability of the polysiloxane modified resin.
Addition polymers comprising polysiloxane moieties are described in, e.g., EP-A 300 426, EP-A 361 522, EP-A 413 604 and EP-A 441 276. In EP-A 300 426 the preparation of addition polymers of unsaturated polysiloxanes and .alpha., .beta. ethylenically unsaturated monomers is described. This reaction gives rise to graft-polymers where the polysiloxane moieties are contained in side chains. The product is used as lubricant in electrophotographic photosensitive members. In EP-A 361 522 it is disclosed to produce a macromonomer by introducing a vinyl silane in a terminal diol-type polydimethylsiloxane and radical polymerizing said macromonomer with, e.g. vinylacetate or other .alpha., .beta. ethylenically unsaturated monomers.
In EP-A 581 150 it is disclosed to form a releasing agent for blending in to toner particles by reacting an organic polysiloxane having an hydroxyl group or an epoxy group with an ethylenically unsaturated dicarboxylic acid grafted polyolefin or with a reaction product of said grafted polyolefin and an active hydrogen atom containing compound selected from the group consisting of an alcohol, an amine and an aminoalcohol. The polyolefin used in the reaction is preferably a low molecular weight polyolefin. This release agent is basically a crystalline polymer and by mixing this releasing agent with toner resins, the toner resin/releasing agent system shows incompatibilities, since the releasing agents in this disclosure are very apolar and since, due to the crystallinity of this releasing agent, the interfacial adhesion to the toner resin is very low. When using such a toner resin/releasing agent system in a process for toner preparation wherein the toner particles are prepared by a pulverizing process, the releasing agent tends to break out of the mixture, thus forming free particles of releasing agent during the pulverizing step. This free particles of releasing agent can not easily be controlled and are inevitably introduced together with the toner particles in the developer, thus inducing unstable behaviour of the developer.
There is thus still a need, to enhance the releasing properties of toner particles for a polysiloxane modified resin that could be incorporated in toner resin in higher amounts than previously disclosed and thus further enhancing the releasing properties of toner particles, without however negatively influencing the physical properties of the toner particles and showing a better compatibility and interaction with commonly used toner resins.
Most preparation methods for polysiloxane modified resins are adapted for the formation of either modified polycondensation copolymers or modified addition copolymers. A single method that makes it possible to form both modified polycondensation copolymers or modified addition copolymers, has not been found.
The reactions often proceed in organic solvents, which have to be recuperated for complying with environmental legislation, or when the reactions proceed in the melt, the preparation of copolymers comprising polysiloxane moieties are mostly conducted at high temperature and there is a risk of degradation of the polysiloxane moiety.
There is also thus still need for an easy, fast, reproducible and solvent free preparation method, that is applicable both for forming polysiloxane modified polycondensation copolymers and addition copolymers.